Most modern-day Constructs look like suits of plate mail with nothing inside. However, since Constructs are not biological entities, they can actually take any form. They can be made from stone, wood, metal, or plastic. They can be small enough to fit in one's hand, or they can be as large as a house. A Construct usually looks humanoid in some fashion, but they don't have to.
What separates Constructs from ordinary machines is the ability to think. While a Construct's mind is often vastly inferior to that of a Human's, they do have problem-solving skills, can reason, and can make logical decisions. Most Constructs are emotionless.
Older Constructs may look like robots (i.e. have sensor arrays and blinking lights protruding from their carapace. Still others may take on the appearance of vehicles, such as trucks or aircraft.
Because Constructs have no biology, their power must come from other sources. Modern Constructs are usually powered by a Mathematician's Theoretical Engine (a purely mathematical contrivance that somehow pulls energy out of the universe in small quantities.) Older Constructs may be powered by solar, fusion, or nuclear fission.
Constructs are slow and tough. They are rarely leaders, but, if treated well, can display incredible loyalty, tenacity, and courage. Due to their low Wisdom, most Constructs suffer from acting first, thinking second. They never need to sleep and are immune to most mind-altering spells. Constructs get along best with Dwarves.